Apparatus

ABSTRACT

The disclosure relates to an apparatus including a first heat transfer element having a base plate, with a first surface for receiving an electric component and channels for transferring a heat load received via the first surface into a fluid in the channels, at least some of the channels protrude from a second surface of the base plate, and a second heat transfer element for receiving fluid from the first heat transfer element and passing a heat load from said fluid to surroundings. In order to obtain an efficient cooling, a phase change material is arranged at a second surface of the base plate between at least two of the channels, the phase change material absorbing heat by changing phase at a phase change temperature during operation of the electric component.

RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. §119 to European Patent Application No. 11180187.4 filed in Europe on Sep. 6, 2011, the entire content of which is hereby incorporated by reference in its entirety.

FIELD

This disclosure relates to an apparatus to be cooled, and to a cooling solution for an apparatus including electric components.

BACKGROUND INFORMATION

A known apparatus with a heat exchanger having a first heat transfer element includes a base plate for an electric component, and channels for transferring a heat load from the base plate into fluid in the channels. The fluid can be passed on via the channels to a second heat exchanger where the fluid can be cooled. At least some of the channels protrude from a surface of the base plate.

The heat exchanger can have insufficient heat storage capacity especially for handling temporary peaks in the amount of heat generated by electric components.

SUMMARY

An apparatus is disclosed comprising a first heat transfer element including a base plate, with a first surface for receiving an electric component and channels for transferring a heat load received via the first surface into a fluid in the channels, at least some of the channels protruding from a second surface of the base plate, a second heat transfer element for receiving fluid from the first heat transfer element and for passing a heat load from the fluid to the surroundings, and a phase change material arranged at the second surface of the base plate between at least two of the channels, the phase change material absorbing heat by changing phase at a phase change temperature during the operation of said electric component.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present disclosure will be described in closer detail by way of example and with reference to the attached drawings, in which

FIGS. 1 to 2 illustrate a first exemplary embodiment of an apparatus according to the disclosure;

FIG. 3 illustrates an exemplary embodiment of the apparatus of FIGS. 1 and 2 with a phase change material;

FIG. 4 illustrates a temperature difference obtained with the apparatus of FIGS. 1 and 2;

FIG. 5 illustrates a second exemplary embodiment of an apparatus according to the disclosure; and

FIGS. 6 to 8 illustrate an effect of phase change material at different ambient temperatures.

DETAILED DESCRIPTION

The use of a phase change material which during a phase change absorbs heat can make it possible to obtain an apparatus with more efficient cooling. Such a phase change material can be arranged in a well-protected space between at least two channels in order to temporarily provide a higher cooling capacity due to a phase change of the material. Once there is no longer a need for a higher cooling capacity and the temperature reaches a level below the phase change temperature, the phase change material can return to the original physical state in order for it to be ready to absorb excess heat during a subsequent peak in the heat generation.

In an exemplary embodiment, a cooling apparatus can be adjusted in order to keep a temperature such that the phase change material will work optimally.

FIGS. 1 to 2 illustrate a first exemplary embodiment of an apparatus 1 according to the disclosure. The apparatus includes a first heat transfer element 2 having a base plate 3 with a first surface 4 for receiving one or more electric components that require cooling during their use in order to avoid an excessive temperature rise. The first heat transfer element 2 also includes a plurality of channels 5 for transferring a received heat load into a fluid circulating in the channels. From FIG. 2 it can be seen that in this embodiment the channels 5 can be arranged in pipes 6, which are spaced apart and have internal walls separating a plurality of channels 5 from each other. The pipes can be MPE (MultiPort Extruded) pipes which have been manufactured by extruding aluminum, for example. In FIG. 1 the apparatus 1 is seen from a direction where the base plate 3 is on top of the pipes 6 and FIG. 2 illustrates only some of the parts of the apparatus 1 seen from a direction where the pipes 6 are on top of the base plate 3.

The apparatus includes a second heat transfer element 7, which receives fluid from the first heat transfer element 2. In this exemplary embodiment the pipes 6 extend all the way from a first manifold 8 arranged in the proximity of the first heat transfer element 2 to a second manifold 9 arranged in the proximity of the second heat transfer element 7. The second heat transfer element 7 includes the pipes 6 and fins 10 which extend between the channels 5, in this case the walls of the pipes 6 containing the channels. An airstream passing through the second heat transfer element 7 can therefore transfer heat away from the fluid in the pipes 6.

In the illustrated embodiment, the apparatus 1 can work as a thermosyphon. The pipes 6 partly penetrate into the base plate 3 (working as an evaporator) such that some of the channels 5 located in the pipes can be evaporator channels containing fluid that is heated when the first heat transfer element 2 receives heat from an electric component. The heated fluid (or possibly vapor at this stage) flows towards the second heat transfer element 7 (working as a condenser), where air passing between the channels 5 (located inside the pipes 6) cools the fluid. The second manifold 9 can be implemented as a tank, for example, a closed space with a fluid connection to all channels 5 of the pipes 6. The fluid can therefore exit the evaporator channels into the manifold and return downwards towards the first manifold 8 via those channels 5 of the pipes 6 that are located outside the base plate 3 and function as condenser channels. The first manifold 8 can be implemented similarly to the second manifold 9, for example, as a tank with a fluid connection to each channel 5 of the pipes. Therefore, the fluid entering the first manifold 8 via the condenser channels can proceed via the evaporator channels to a new flow cycle. Such a thermosyphon is advantageous as it can be utilized for cooling an electric apparatus without a need for a pump to obtain the desired fluid circulation.

An alternative to the illustrated embodiment can be to separate the first and second heat transfer element 2 and 7 from each other. In that case, the parallel channels 5 do not extend all the way between the first and second heat transfer element 2 and 7. Instead, an additional manifold can be arranged in the upper part of the first heat transfer element 2 to receive fluid from all of the channels 5 in the first heat transfer element 2. Similarly, a second additional manifold can be arranged in the lower part of the second heat transfer element 7 to pass fluid to all channels 5 of the second heat transfer element 7. These additional manifolds can be connected to each other with one or more pipes for passing fluid from the first heat transfer element 2 (evaporator) to the second heat transfer element 7 (condenser), and the second manifold 9 can be connected to the first manifold 8 via one or more additional pipes for returning the fluid from the second heat transfer element 7 (condenser) to the first heat transfer element 2 (evaporator).

Irrespective of which of the implementations is used for the thermosyphon, the first heat transfer element 2 can be provided with a phase change material 11 which during operation of the apparatus enters a phase change to absorb heat in order to cool the base plate 2 and one or more electric components attached to the base plate. Such a phase change material 11 can be arranged against a second surface 12 of the base plate 3, for example, substantially over the entire surface area of the base plate 3. The second surface 12 of the base plate 3 in the illustrated embodiment is provided with channels 5 contained in pipes 6 and with fins 10 extending between these channels. However, there can be a lot of empty spaces delimited by the second surface 12, the channels 5 and the fins 10, and for example, as many of these empty spaces as possible can be filled with the phase change material. In such an arrangement, the phase change material can be efficiently protected. Heat can be conducted directly from the base plate 3 to the pipes 6 containing channels 5 and fluid, and in addition, from the base plate 3 via the fins 10 to the pipes 6. In order to work as efficiently as possible, the phase change material should be located thermally closer to heat source than the “main” cooling system is. In this way the phase change material reacts faster than the main cooling system to temperature changes.

A Phase Change Material (PCM) can be a substance, which by changing phase at a certain constant temperature, called phase change temperature, is capable of storing and releasing large amounts of energy at constant temperature. Phase change can occur as melting and solidifying or as changes in the crystal structure of materials where the phase change takes place from solid to solid. Heat can be absorbed or released when the material changes from one phase to another. Initially the temperature of a phase change material 11 rises as the phase change material absorbs heat. However, when a phase change material reaches a phase change temperature at which it changes phase, it can absorb large amounts of heat at a constant temperature until all material is transformed to the new phase. When the ambient temperature around the material subsequently falls, the phase change material can return to its previous physical state, and release its stored latent heat.

A large number of phase change materials are available on the market in any required temperature range, for example, from 114° C. up to 1010° C. A common type of phase change materials is the solid-liquid. There are, however, other types of phase change materials and some materials exhibit solid-solid phase changes, in which the crystalline structure is altered at a certain temperature. To be a useful PCM, a material should ideally meet several criteria, release and absorb large amounts of energy when freezing and melting, have a fixed and clearly determined phase change temperature, remain stable and unchanged over many freeze/melt cycles, be non-Hazardous, be economical, and should not cause corrosion problems to other materials.

In the illustrated embodiment the apparatus 1 can be used in an upright position, due to which a phase change material 11 with a solid-solid phase change is desirable. Such a phase change material 11 can be inserted directly between the channels 5 and the fins 10 as illustrated in FIG. 2. Examples of suitable materials are salt hydrates, fatty acids, esters, and various paraffins (such as octadecane).

FIG. 3 illustrates an alternative for providing the apparatus of FIGS. 1 and 2 with a phase change material.

In FIG. 3 a container 13 is used for encapsulating the phase change material 11 before it is arranged in its place on the second surface 12 of the base plate. This gives a greater freedom in selecting a suitable phase change material. Solid-liquid phase change materials, for example, can be used as the phase change material and can be hermetically sealed. A suitable material to be used in the embodiment of FIG. 3 can be, for example, salt hydrate, such as PlusICE X80, available from Phase Change Material Products Limited, for instance.

If solid-liquid material is used, the “container” can be implemented to include the baseplate 3, the pipes 6 and a lid which create a container or tank for the phase change material.

In the exemplary embodiment of FIG. 3, no fins 10 are arranged at the location of the second surface 12 reserved for the container 13. However, if it is advantageous to use fins 10 also in connection with one or more containers 13 with phase change material 11, then the fins 10 can be arranged inside the container 13 together with the phase change material 11. A container 13′ containing both phase change material 11 and fins 10 is also illustrated in FIG. 3.

The fins 10 should be (thermally) attached to the base plate 4 via the second surface 12, so that the heat from the heat source can come via baseplate 4 to fins 10 and further to the phase change material. The fins 10 provide a good and even contact to the phase change material, so that the heat distribution to the phase change material is as even as possible.

Some of the available solid-solid phase change materials have a very poor thermal conductivity, which means that the effective thickness (=heat path) can be only a few millimeters. It is desirable that the heat path from heat source to the phase change material is as short as possible and the contact area to the phase change material is as big as possible. The structure described above utilizing fins to conduct heat from the base plate into the phase change material is good from this point of view.

FIG. 4 illustrates the temperature difference obtained with the apparatus of FIGS. 1 and 2.

FIG. 4 illustrates the temperature T (the temperature probe is located on the surface 4 just below the heat source) at different moments of time t (seconds) when the apparatus of FIG. 1 is used for removing heat from electronic components of a frequency converter (can be used other electric devices too), for example, a drive used for controlling the speed of an electric motor, for instance. The ambient temperature has been selected to be optimal for the phase change material in question, in this case 40° C. Curve B illustrates the temperature behavior when no phase change material is in use, and the curve A illustrates the temperature behavior when the spaces between the channels 5, the fins 10 and the second surface 12 of the base plate are filled with a phase change material. In this case, the temperature peak is reduced (ΔT) by about 6.4° C.

For semiconductor components, for example, a reduction of the temperature change can have a significant impact on the expected lifetime of the component in question. Practical tests have shown that when temperature peaks occur cyclically, a reduction of the temperature change during the peak from 30° C. to 25° C. increases the number of cycles without malfunctions by about 4 to 5 times.

Also the peak temperature will be lower (in this example from 77-71° C.), which also makes the lifetime longer.

FIG. 5 illustrates a second exemplary embodiment of an apparatus 1′. The apparatus 1′ is very similar to the one explained in connection with FIGS. 1 and 2. Therefore the embodiment of FIG. 5 will mainly be explained by pointing out the differences between these embodiments.

In FIG. 5, a similar apparatus, for example, thermosyphon with a base plate 3, a second heat transfer element 7, channels 5 and manifolds 8 and 9 is used as in FIG. 1. The second surface of the base plate (not shown in FIG. 5) can also be provided with a phase change material.

Phase change materials can be efficiently utilized at an ambient temperature which is dependent on the selected material in question. Each phase change material has a different phase change temperature and can be selected depending on the application. Properties and the amount of phase change material is always dependent on the design (system), heat load, allowed temperatures and cooling conditions (ambient temperature or cooling temperature). To achieve the best results, the phase change temperature of the phase change material should be selected accordingly.

The best results in using a phase change material can be obtained by ensuring that the ambient temperature is optimal for the selected phase change material. FIG. 5 illustrates two alternatives that can be used simultaneously or independently of each other for ensuring that the ambient temperature is optimal. In both alternatives a temperature sensor 14 can be utilized for measuring the ambient temperature and information about the ambient temperature is provided to a controller 15, which may be implemented with circuitry or as a combination of circuitry and a computer program. In many cases the controller is integrated to circuitry of electric device, so that it does not require any extra components and/or printed circuit boards. In these cases the functionality is done with software.

The controller can also be implemented by at least one processor (e.g., general purpose or application specific) or a computer processing device which is configured to execute a computer program tangibly recorded on a non-transitory computer-readable recording medium, such as a hard disk drive, flash memory, optical memory or any other type of non-volatile memory. Upon executing the program, the at least one processor is configured to perform the operative functions of the above-described exemplary embodiments.

The temperature sensor 14 can be attached to an electric component 16, the base plate 3, the phase change material or the second heat transfer element 7. In general, the temperature sensor should desirably be placed as close to the actual heat source as possible in order to detect changes as fast as possible. The controller receives information about the measured temperature, which is used by the controller 15 to determine if the measured temperature is above or below a reference temperature (the optimal ambient temperature for the selected phase change material in question).

The first alternative is that the controller 15 adjusts the cooling efficiency in order to try to maintain the ambient temperature at the optimal level. In that case, an adjustable fan 17 may be utilized, for instance, in order to increase or decrease the amount of air flowing through the second heat transfer element 7. If the measured temperature is too high, the speed of the fan 17 is increased, and if the measured temperature is too low, the speed of the fan 17 is reduced. Depending on the practical implementation, other types of adjustable cooling may be employed, in which case the adjustment can affect the speed of a pump or the position of a valve regulating a flow, for instance. If a pump is utilized the cooling media flowing between the channels of the second heat transfer element may be a suitable liquid such as water, for instance.

The second alternative is that the controller 15 adjusts the amount of heat produced by the electric component 16. In that case, the controller 15 controls the electric component or components to operate in a mode (at a lower efficiency level, for example) where they produce less heat during periods when the measured temperature is too high. In the case of a frequency converter, for example, this might lead to a situation where the entire potential of the frequency converter cannot be utilized during such periods but permanent damage to the components of the frequency converter can in any case be avoided. The use of the phase change material can make it possible to allow a bigger heat peak than in solutions without the phase change material.

FIGS. 6 to 8 illustrate the effect of phase change material at different temperatures. FIGS. 6 to 8 are similar to FIG. 4. Thus they illustrate the temperature T at different moments of time t (seconds) when the apparatus of FIG. 1 is used for removing heat from electronic components. Curve B illustrates the temperature behavior when no phase change material is in use, and the curve A illustrates the temperature behavior when the spaces between channels 5, the fins 10 and the second surface 12 of the base plate are filled with a phase change material. The used phase change material is the same in FIGS. 4 and 6 to 8.

In the case of FIG. 4, the exemplary ambient temperature was selected to be optimal for the phase change material, for example 40° C. In that case, the temperature peak was reduced (ΔT) by about 6.4° C. when phase change material was in use.

In the case of FIG. 6, the exemplary ambient temperature is no longer optimal, but instead 30° C. In that case, the temperature peak was reduced (ΔT) by about 1.2° C. when phase change material was in use.

In the case of FIG. 7, the exemplary ambient temperature is 35° C. In that case, the temperature peak was reduced (ΔT) by about 3.9° C. when phase change material was in use.

In the case of FIG. 8, the exemplary ambient temperature is 45° C. As can be seen from FIG. 8, the phase change material changes phase early at this temperature, and after about 75 seconds the phase change has already taken place.

Based on a comparison of FIGS. 4 and 6 to 8 it is clear that in order to work efficiently, the phase change material desirably should be used at an ambient temperature optimal for the material in question, otherwise there is not much sense in utilizing phase change material at all. Based on this discovery, it is clear that a solution where the “main” cooling system is adjusted in order to keep the temperature at a suitable level for the phase change material, as explained in connection with FIG. 5, can be advantageous, because then once a peak occurs in the heat generation, the phase change material can work efficiently and quickly to reduce the negative impact such a peak can have on the apparatus in question. If the pump (and liquid) is used instead of the fan (and air), there is analogue from ambient temperature to coolant (e.g. water) temperature.

It is to be understood that the above description and the accompanying figures are only intended to illustrate the present disclosure. It will be obvious to a person skilled in the art that the disclosure can be varied and modified without departing from the scope of the disclosure.

Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein. 

What is claimed is:
 1. An apparatus comprising: a first heat transfer element including a base plate, with a first surface for receiving an electric component and channels for transferring a heat load received via the first surface into a fluid in the channels, at least some of the channels protruding from a second surface of the base plate; a second heat transfer element for receiving fluid from the first heat transfer element and for passing a heat load from the fluid to the surroundings; and a phase change material arranged at the second surface of the base plate between at least two of the channels, the phase change material absorbing heat by changing phase at a phase change temperature during the operation of said electric component.
 2. The apparatus according to claim 1, wherein the second heat transfer element comprises: channels for receiving the fluid from the first heat transfer element; and fins extending between the channels for transferring the heat load to air passing between the channels.
 3. The apparatus according to claim 1, wherein the second heat transfer element comprises: channels for receiving the fluid from the first heat transfer element; and a cooling liquid passing between the channels for transferring the heat load from the channels to the passing cooling liquid.
 4. The apparatus according to claim 1, comprising: a first manifold arranged in the proximity of the first heat transfer element; a second manifold, arranged in the proximity of the second heat transfer element; the first and second manifolds connecting the channels to each other at respective opposite ends of the channels; wherein the channels extend between the first manifold and the second manifold.
 5. The apparatus according to claim 1, wherein the first heat transfer element comprises fins extending between the channels.
 6. The apparatus according to claim 1, wherein the channels are arranged in pipes, the pipes are spaced apart and have internal walls separating a plurality of channels from each other.
 7. The apparatus according to claim 1, wherein the phase change material is a material in which the heat absorption occurs during a phase change from a solid state to a solid state.
 8. The apparatus according to claim 1, wherein the phase change material is arranged in a container.
 9. The apparatus according to claim 1, wherein the phase change material is arranged in a container comprising fins.
 10. The apparatus according to claim 1, comprising: a temperature sensor for measuring a temperature; an adjustable cooling arrangement; and a controller, responsive to the temperature sensor, for comparing the temperature measured with the temperature sensor to a reference temperature, and for controlling the adjustable cooling arrangement to reduce or increase cooling in order for the measured temperature to reach the reference temperature.
 11. The apparatus according to claim 1, comprising: a temperature sensor for measuring a temperature; and a controller, responsive to the temperature sensor, for comparing the temperature measured with the temperature sensor to a reference temperature, and for controlling one or more electric components of the apparatus to operate in a mode where they produce less heat when the measured temperature is higher than the reference temperature.
 12. The apparatus according to claim 10, wherein the temperature sensor for measuring the temperature measures the temperature of an electric component attached to the base plate, the temperature of the base plate, the temperature of the phase change material or the temperature of the second heat transfer element.
 13. The apparatus according to claim 11, wherein the temperature sensor for measuring the temperature measures the temperature of an electric component attached to the base plate, the temperature of the base plate, the temperature of the phase change material or the temperature of the second heat transfer element.
 14. The apparatus according to claim 1, in combination with a frequency converter or inverter. 